[llvm] [AMDGPU] Handle subregisters properly in generic operand legalizer (PR #108496)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Aditi Medhane (AditiRM)

<details>
<summary>Changes</summary>

Fix for the issue found during COPY introduction during legalization of PHI operands for sgpr to vgpr copy when subreg is involved

---
Full diff: https://github.com/llvm/llvm-project/pull/108496.diff


2 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/SIInstrInfo.cpp (+2-1) 
- (modified) llvm/test/CodeGen/AMDGPU/phi-vgpr-input-moveimm.mir (+2-2) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index e4a679f6a3ef8f..2102c608f8cb21 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -6231,10 +6231,11 @@ void SIInstrInfo::legalizeGenericOperand(MachineBasicBlock &InsertMBB,
     return;
 
   Register DstReg = MRI.createVirtualRegister(DstRC);
+  Op.setSubReg(0);
   auto Copy = BuildMI(InsertMBB, I, DL, get(AMDGPU::COPY), DstReg).add(Op);
 
   Op.setReg(DstReg);
-  Op.setSubReg(0);
+  Op.setSubReg(OpSubReg);
 
   MachineInstr *Def = MRI.getVRegDef(OpReg);
   if (!Def)
diff --git a/llvm/test/CodeGen/AMDGPU/phi-vgpr-input-moveimm.mir b/llvm/test/CodeGen/AMDGPU/phi-vgpr-input-moveimm.mir
index dab4c9d401407b..d21dbd290accea 100644
--- a/llvm/test/CodeGen/AMDGPU/phi-vgpr-input-moveimm.mir
+++ b/llvm/test/CodeGen/AMDGPU/phi-vgpr-input-moveimm.mir
@@ -73,13 +73,13 @@ body:             |
   ; GCN-NEXT:   successors: %bb.2(0x80000000)
   ; GCN-NEXT: {{  $}}
   ; GCN-NEXT:   [[S_ADD_U:%[0-9]+]]:sreg_64 = S_ADD_U64_PSEUDO [[COPY]], [[COPY1]], implicit-def $scc
-  ; GCN-NEXT:   [[COPY2:%[0-9]+]]:vreg_64 = COPY [[S_ADD_U]].sub0, implicit $exec
+  ; GCN-NEXT:   [[COPY2:%[0-9]+]]:vreg_64 = COPY [[S_ADD_U]], implicit $exec
   ; GCN-NEXT:   S_BRANCH %bb.2
   ; GCN-NEXT: {{  $}}
   ; GCN-NEXT: bb.2:
   ; GCN-NEXT:   successors: %bb.3(0x80000000)
   ; GCN-NEXT: {{  $}}
-  ; GCN-NEXT:   [[PHI:%[0-9]+]]:vgpr_32 = PHI [[V_MOV_B64_e32_]].sub0, %bb.3, [[COPY2]], %bb.1
+  ; GCN-NEXT:   [[PHI:%[0-9]+]]:vgpr_32 = PHI [[V_MOV_B64_e32_]].sub0, %bb.3, [[COPY2]].sub0, %bb.1
   ; GCN-NEXT:   S_BRANCH %bb.3
   ; GCN-NEXT: {{  $}}
   ; GCN-NEXT: bb.3:

``````````

</details>


https://github.com/llvm/llvm-project/pull/108496